1. Field of the Invention
The present invention relates to a system which enables the reuse of water soluble slurry waste fluid used when brittle materials, for example, semiconductor ingots such as compound semiconductor crystal ingots and silicon semiconductor crystal ingots are sliced with a wire saw slicing apparatus.
2. Description of the Related Art
There is known a wire saw slicing apparatus as a means for slicing brittle materials such as compound semiconductor crystal ingots and silicon semiconductor crystal ingots. The wire saw slicing apparatus, as shown in FIG. 4, includes three plastic main rollers 10A, 10B and 10C of the identical construction disposed with their axes parallel spaced from one another, and a wire 12 wound spirally around helical grooves 14a, 14b and 14c formed at regular intervals or pitches in the respective outer peripheral surfaces of the main rollers 10A-10C. The main rollers may be plural in number and should by no means be limited to any particular number, but four or three main rollers as in the illustrated embodiment are 25 used in general. The main roller 10C constitutes a drive roller and is connected in driven relation to a drive motor 16. A rotary motion of the main roller 10C is transmitted via the wire 12 to the remaining main rollers 10A, 10B which constitute driven rollers.
The wire 12 has one or a leading end portion wound around a wire reel bobbin 22 via a tension adjustment mechanism 20. The wire reel bobbin 22 is rotatably driven by a torque motor 24. A tension on a portion of the wire 12 extending between the tension adjustment mechanism 20 and the wire reel bobbin 22 is regulated according to a voltage applied to the torque motor 24. And, a tension on a portion of the wire 12 running between the tension adjustment mechanism 20 and the drive roller 10C is adjusted at a constant value by the tension adjustment mechanism 20.
Similarly, the opposite or a trailing end portion of the wire 12 is wound around a wire reel bobbin 32 via a tension adjustment mechanism 30. The wire reel bobbin 32 is rotatably driven by a torque motor 34. A tension on a portion of the wire 12 extending between the tension adjustment mechanism 30 and the wire reel bobbin 32 is regulated according to a voltage applied to the torque motor 34. And, a tension on a portion of the wire 12 running between the tension adjustment mechanism 30 and the drive roller 10C is adjusted at a constant value by the tension adjustment mechanism 30.
A workpiece 40 is composed, for example, of a semiconductor single crystal ingot having an orientation flat and attached by bonding to a workpiece holder 42 via the orientation flat. The workpiece holder 42 is vertically moved up and down along a linear path.
The wire saw slicing apparatus of the above construction operates as follows. The drive roller 10C is rotated by the drive motor 16 to reciprocate the wire 12 in the axial or longitudinal direction thereof. A working fluid containing abrasive grains is supplied to a contact area between workpiece 40 and the wire 12. While keeping this condition, the workpiece 40 is further moved downwards whereby the workpiece 40 is sliced at one time into a multiplicity of wafers by a lapping action attained by the reciprocating wire 12 and the abrasive-containing working fluid supplied thereto.
An oily slurry, which contains oil (oily coolant) based on mineral oil and abrasive grains as of SiC, is used as the above-mentioned working fluid. However, when this oily slurry is used, there are inconveniences in cleaning a workpiece sliced with the wire saw slicing apparatus, disposing of the used oily slurry or the oily slurry waste fluid, etc. That is, although it is efficient to use an organic solvent in order to clean the workpiece sliced by the use of the oily slurry, the organic solvent can not be used from the viewpoint of an environmental problem. In conventional disposal methods, the oily slurry waste fluid has been predominantly burnt as industrial waste. However, since carbon dioxide (CO.sub.2) generated when burning the oily slurry waste fluid is listed as a cause of environmental problems such as earth warming, the burning thereof is not desirable.
Then water soluble coolant has been developed as a substitute of the oily coolant to cope with the environmental problem. A water soluble slurry which contains the water soluble coolant and abrasive grains as of SiC has been recently used as a working fluid when slicing semiconductor ingots or the like with the wire saw slicing apparatus. The newly developed water soluble coolant has a problem that the cost thereof becomes higher because of the following reasons. Since the rate of the abrasive grains which actually contribute to the slicing operation in the total abrasive grains contained in the water soluble slurry is very low, many of the abrasive grains in the water soluble slurry waste fluid after completion of the slicing operation are in the condition of being available or usable. However, this water soluble slurry waste is discarded with such available abrasive grains, and thereby the total slicing cost has been greatly raised. In addition, the water soluble slurry waste fluid is usually treated by an activated sludge method in a waste water disposal plant but a big load to treat the water soluble slurry waste fluid falls thereon. So there is a problem that all of the water soluble slurry waste fluid can not be sent thereto.